The present invention relates to apparatus for mechanical purification of waste water, especially for mechanical purification of biologically purified waste water.
It is already known to provide an apparatus for mechanical purification of waste water with one or more hollow-drum-shaped rotary frames for filters which permit water to flow into the interior of the frames but intercept the impurities so that each filter gradually accumulates a layer of intercepted contaminants and its filtering action deteriorates accordingly. It is also known to clean such filters at required intervals by streams of clean water which are directed against the inner sides of the filters and cause the separated contaminants to enter the inlets of suction heads. Reference may be had to U.S. Pat. No. 4,090,965.
The versatility of the apparatus which is disclosed in the German patent is insufficient, mainly because the cleaning action is unsatisfactory so that the permeability of the filters deviates from an optimum permeability. Attempts to intensify the cleaning action include the provision of means for spraying clean water against the inner sides of the filters and the provision of pumps which remove water from the outer sides of the filters in the course of the spraying operation. Such apparatus are bulky, complex and expensive. Moreover, the energy requirements of conventional apparatus are high and their capacity is small.